Process for separation of alkyl phenols by azeotropic distillation with a 10-13 carbon atom alkene



Dec. 9, 1969 L. L. PARISSE PROCESS FOR SEPARATION OF ALKYL PHENOLS BYAZEOTROPIC DISTTLLATION WITH A 10-15 CARBON ATOM ALKENE Filed May 28,1968 ALKYL PHENOLS NON -POLAR ALKE POLAR ALXIIIIS PHENOLS NON POLARNON-POLAR ALKYL PHENOLS ALKENE AZEOTROPIC DISTILLATION AZEOTROPE OFPOLAR NON-POLAR AND NE ALKYL PHENOLS POLAR ALKYL PHENOLS NON-POLARALKENE INVENTOR. LOU/S L. PAP/SSE his United States Patent Aug. 13,1985, has been disclaimed and dedicated to the Public Int. Cl. B01d3/36, 3/34 U.S. Cl. 203-70 9 Claims ABSTRACT OF THE DISCLOSURE Polaralkyl phenols preferentially azeotrope with a non-polar alkene so thatthe azeotroped alkyl phenol is separable by distillation from less polaralkyl phenols. The non-polar alkene should have about 12 carbon atomsand its boiling point should be within 30 C. of the alkyl phenol withwhich it is to azeotrope.

CROSS-REFERENCE This application is a continuation-in-part ofapplication Ser. No. 600,492, filed Dec. 9, 1966.

BACKGROUND OF THE INVENTION This invention relates to a process for theseparation and purification of alkyl phenols, particularly, to theseparation of alkyl phenols from a mixture of alkyl phenols having closeboiling points but difiering degrees of polarity by adding to themixture an azeotroping agent which preferentially azeotropes at leastone of the alkyl phenols.

Monoand polymethyl phenols are naturally occurring phenols found in coaltar distillates such as derived from bituminous coal. Dimethyl phenols,as well as trimethyl phenols, are also obtained as by-products in thealkylation of phenol to produce 2-methyl phenol (o-cresol). The dimethylphenols exist in six isomeric forms, as do also the trimethyl phenols.

Certain of the methylphenol isomers are valuable as intermediates forthe synthesis of, for example, antioxidants, while others may be used aspolymerizable monomers. For example, 2,6-dimethyl phenol is a valuableisomer which is used in the preparation of aromatic polyethers such aspolyphenylene oxide. It is, therefore, desirable to obtain the isomer ina highly purified form. Unfortunately, when 2,6-dimethyl phenol isproduced synthetically or is produced from coal tar distillates,monomethyl phenols (cresols) are present. For example, when 2,6-dimethylphenol is present in what is called the cresol distillate or fraction ofcoal tar by-product-named for the monomethyl phenols (cresols) which arein this fraction-it is almost impossible to separate the 3-methyl phenoland 4-methyl phenol from the dimethyl phenol by ordinary distillationtechniques due to the close boiling points of the compounds, (201 C. for2,6-dimethyl phenol, 208.8 C. for B-methyl phenol, and 202.5 C. for4-methyl phenol.)

SUMMARY OF THE INVENTION It has now been discovered that alkyl phenolmixtures having very close boiling points may be separated by theaddition of an alkene azeotroping agent to the mixture.

In accordance with the invention, alkyl phenols having close boilingpoints may be separated by:

(a) Adding to a mixture of alkyl phenols wherein at least one alkylphenol is more polar than the others, a non-polar higher alkene having aboiling point within about 30 C. of the more polar alkyl phenol to forman azeotrope of the alkene and the more polar alkyl phenol.

(b) distilling the mixture to separate the azeotrope from the less polaralkyl phenol.

DETAILED DESCRIPTION While the exact mechanism by which the alkenepreferentially azeotropes with one or more of the alkyl phenols is notcompletely understood, it is believed that the alkene, being a non-polarmolecule, is preferentially attracted to the most polar alkyl phenol orphenols, for example, to 3-methyl phenol and 4-methyl phenol rather than2,6-dimethyl phenol due to the steric hindrance and thus low polarity ofthe 2,6-dimethyl phenol.

The higher alkenes useful in this invention are those having from 10-13and preferably 12 carbon atoms. The particular alkene selected shouldhave a boiling point within about 30 C. of the polar alkyl phenol withwhich it is to form an azeotrope.

Examples of suitable higher alkenes are those formed by trimerization ofmethylpropene (iso-butylene); decenc- 1; dodecene-l; and propylenetetramer. The trimers of methylpropene may be obtained as a by-productin the butylation of cresols with iso-butylene to produce butylcresols.If the trimer be obtained in this fashion, it may be purified to removecresylic impurities by caustic scrubbing followed by fractionaldistillation.

In accordance with the invention, the boiling point of the non polaralkene azeotroping agent must be within about 30 C. of the polar alkylphenol or phenols with which it is to azeotrope. The boiling points ofthe examples mentioned above are:

The alkene-polar alkyl phenol azeotrope contains about -90% by weightalkene at atmospheric pressure. It is, therefore, necessary, when thedistillation is conducted at atmospheric pressure, to use amounts ofalkene in a weight ratio to the polar alkyl phenol with which it is toazeotrope of at least 6 to 1. However, since the weight percent of thealkene in the azeotrope decreases with pressure, lesser amounts ofalkene can be used if the distillation is carried out at higherpressures. It is preferable to add an excess of alkene usually about 10to 1 to 20 to 1 for atmospheric distillations. The excess alkene is thenremoved in the distillaiton after the alkenepolar alkyl phenolazeotrope. Some of the less polar alkyl phenol may also come over inthis fraction in which case, the fraction may be recycled to increasethe overall yield.

After the azeotropic distillation, the azeotroped alkyl phenol may beseparated from the alkene by conventional means such as steamdistillation or crystallization.

The accompanying flow sheet and the following examples will serve tofurther illustrate the practice of the invention.

Example I 200 grams of a C branched alkene (trimer of iso-butylene) wasadded to 200 grams of a mixture of 2,6-dimethyl phenol and monomethylphenols which had been previously analyzed and found to contain 91.5%2,6-dimethyl phenol, 1.9% Z-methyl phenol, and 6.6% 3- methyl phenol and4-methyl phenol. The mixture was pumped to a still equipped with ahelix-packed distillation column. The mixture was distilled atatmospheric pressure with a 19:1 reflux ratio. The first series of cutswere was added to 200 grams of crude 2,6-dimethyl phenol (2,6-xylenol)having an analysis as follows:

collected up to a boiling point of 176 C. A second series Percent ofcuts were then collected between 176 and 200 C. 2,6-dirnethyl phenol93.5 The third series of cuts were collected at 201 C. Analysis 2-methylphenol 2.0 of the fractions by vapor phase chromatography revealed 53-methy1 phenol and 4-methyl phenol 4.1 the following constituents:Phenol -2 0.4

TABLE I Area percent composition Boilin Weight Weight C19 2,(rdimethylZ-methyl 3-rnethyl phenol Fraction point, (g.) (percent) trimer phenolphenol 4-methyl phenol Fractions l-4 contained almost all of themonomethyl The mixture was pumped to a still equipped with a phenolswhile fractions 10 and 11 were essentially pure 25 helix-packdistillation column and distilled at atmospheric 2,6-dirnethyl phenol.Fractions -9 are suitable for repressure (732-742 mm. Hg) with a :1reflux ratio. cycle back to the still or the alkene may be separatedfrom The cut or fractions were collected and analyzed by vapor the2,6-dimethyl phenol by steam distillation. phase chromatograpy asfollows:

TABLE II Area percent composition 3-methyl phenol Boiling Weight Weight2,6-dimethyl 2-rnethyl 4-methy1 Fraction p0int;,C. (g.) (percent)Dodeeeno-l phenol phenol phenol 11 213-220 101 20. 2 100 Residue v- 19 8Similar results are obtained when the weight ratios of Fractions 1-5contain all the phenol and mono-methyl trimer to monomethyl phenolimpurities are varied from phenol impurities. Fractions 6-9 contain pure2,6-dimethyl 6 P3115 y Weight tfimel' P P PS Weight monomethyl phenol ona dodecene-l free basis. It should be noted ph n l mixture to 20 Parts yWalghi mmel P P by here that an excess of dodeccne-l was used. Acut-back Welght 0f monomethyl phenolon total amount of azeotroping agentresults in recovery Example II of pure 2,6-dirnethyl phenol. However,the 2,6-dimethy1 The pure .zfidimethyl phenol Obtained in the thirdphenol is easily recovered. from the alkene by steam disseries of cuts(fractions 10 and 11) in Example I was tillation or by crystallization.further t t P y y obtainingfhe freezlng PP The 2,6-dimetl1yl phenol infractions 6-9 was recovered of the material A ROI-non 9 the hqmd wasPlaced m a by crystallization and a 45.4 C. freezing point detertesttube equipped with a stirrer and a thermometer. The d d h, h d test tubewas immersed in an ice bath while the contents mme m 1691mg 3 P Y P werestirred. When definite crystallization was started, stirring was stoppedand the freezing point considered to Example 1v be the maximumtemperature reached after super cool- The freezing Point was found to be4550 Another azeotropic distillation under the conditions Example III ofExample 111 was carried out using instead of dode- 300 grams ofdodecene4 (obtained f the Gulf cene-l, 300 grams of propylene tetramer(obtained from Oil Corporation) having an analysis as follows: Gulf OilCorporation) having an analysis as follows:

Percent Percent n-Alpha (gefins Mono-olefins 93 Mono-ole ns Di.o1efins 2Saturates Nil Aromatics and di-olefins N11 Aromatics The results of thedistillation are as follows: is selected from the class conslstlng ofdodecene-l,

TABLE III Area percent composition 3- methyl phenol Boiling WeightWeight Propylene 2,6-dimethyl Z-methyl 4-methyl Point, G (g.) (percent)tetrzmer phenol phenol phenol Phenol 163-175 4 0. 8 75. 2 11. 175-185 357 76. 0 7. 1 185-187 87. 5 17. 5 75. 4 21. 3 187 96 19. 1 71. 6 27. 6187-190 38 7. 6 67. 5 32. 5 190-191 53. 5 10. 7 68. 9 31. 1 191-193 76 157. 7 42. 3 193-195 31 6. 1 50. 7 49. 3 195-196 19. 5 3. 9 49. 5 50. 5196-198 7. 5 1. 5 34. 0 66. 0 198-205 38 7. 6 6. 8 93. 2 Residue 11 2. 2

Fractions 5-11 were essentially free of phenolic impurities.2,6-dimethyl phenol crystallized from the propylene tetramer has afreezing point of 45.4 C. As in Example III, the components of thefractions indicate that an excess of the azeotroping agent was used andthat a cut-back would result in recovery of pure 2,6-dimethyl phenol,without the need of further separation from the alkene.

The foregoing has presented a novel process for the separation of polaralkyl phenols from non-polar alkyl phenols which have hitherto been verydifiicultly separable. The process allows, for example, 2,6-dimethylphenol to be separated from mono-methyl phenols with very little loss of2,6-dimethyl phenol.

What is claimed is:

1. A process for the separation of at least two alkyl phenols havingclose boiling points but containing at least one alkyl phenol that ismore polar than the others in the mixture comprising:

(a) adding to said mixture 2. non-polar higher alkene having from 10-13carbon atoms and a boiling point within C. of the said more polar alkylphenol to form an azeotrope of the alkene and the said more polar alkylphenol; and

(b) distilling the azeotrope from said mixture to separate the morepolar alkyl phenol from the less polar alkyl phenol.

2. The process of claim 1 wherein the non-polar alkene has 12 carbonatoms.

3. The process of claim 2 wherein the non-polar alkene decene-l, trimersof methyl-propene, and propylene tetramers.

4. The process of claim 1 wherein the mixtures of alkyl phenolscomprises 2,6-dimethyl phenol and monomethyl phenols.

5. The process of claim 1 wherein the amount of alkene is from 6 to 20times by weight of the weight of the monomethyl phenols present in thealkyl phenol mixture.

6. The process of claim 1 wherein the alkene is dodecene-l.

7. The process of claim 1 wherein the alkene is decene-l.

8. The process of claim 1 wherein the alkene is propylene tetramer.

9. The process of claim 1 wherein said more-polar alkyl phenol isseparated from said non-polar alkene after the distillation.

References Cited UNITED STATES PATENTS 3,207,794 9/1965 Haines et al.203-70 3,337,424 8/1967 Neuworth et al. 260-621 3,397,124 8/1968 Parisse203-52 WILBUR L. BASCOMB, JR., Primary Examiner US. Cl. X.R.

